British intelligence officials have identified the man who killed an American journalist in a brutal beheading video that surfaced last week, NBC News reported Sunday citing unnamed United Kingdom security officials.

NBC News said it has not yet confirmed the name of the suspect seen in the video released by Islamic State militants on Tuesday that shows the killing of James Foley, 40.

Earlier Sunday, British Ambassador to the U.S. Peter Westmacott, told multiple media outlets that officials were "close" to identifying the man.

"We're putting a great deal into the search," he said on CNN's State of the Union, referring to the use of sophisticated technology to analyze the man's voice. Westmacott also spoke on NBC's Meet the Press.

In the video, the man who beheaded Foley is heard speaking with a British accent. Britain's Foreign Secretary Philip Hammond acknowledged last week that the militant in the video could be a British national.

Steven Joel Sotloff, a photojournalist and former University of Central Florida student, remains a hostage of the terrorist group and was threatened with death in the same video.

On Sunday, another kidnapped American journalist was released. Peter Theo Curtis, 45, who writes under the name Theo Padnos, had been held by the al-Nusra Front, a branch of al-Qaeda in Syria.